1. Field of the Invention
This invention relates to trusses and particularly to a new and improved box truss hoop which folds compactly yet which deploys to a large, stiff hoop structure for supporting components such as antenna reflective surfaces.
2. Description of the Prior Art
One type of antenna system employs a reflective surface stretched across a hoop structure. When such antenna systems are to be launched into space, they must be foldable so as to fit into launch vehicles having limited cargo capacity, and, once in space, the antenna system must deploy to a size sufficiently large to justify the cost of launching it.
The reflective surface of the antenna often has a parabolic or spherical shape to reflect radio waves to a receiving element, or feed, mounted ahead of the reflective surface at its focus. Since the reflective surface is flexible so that it can be folded with the hoop structure, it is important that the deployed hoop structure be of sufficient stiffness such that the shape of the reflective surface can be maintained. Additionally, it is desirable that the hoop structure have sufficient depth such that the shaped reflective surface and its shaping system can be substantially contained within the interior of the hoop structure, rather than requiring additional attachment points above or below the hoop.
The requirements for stiffness and depth, however, contrast with another requirement for space antenna systems that the hoop structure be foldable in order to fit into the launch vehicle.
Different configurations of deployable hoop structures have been developed, yet most are unable to fully meet the stiffness, depth and foldablility requirements. Where stiffness and depth are emphasized, the hoop is often bulky and heavy, making it difficult for the hoop to be compactly folded to fit into the launch vehicle. Alternatively, when the hoop is designed to fold compactly, it is often relatively flimsy and shallow, adversely affecting the performance of the antenna.
In view of the above-mentioned problems, it is therefore an object of the present invention to provide a hoop structure with sufficient stiffness to properly support components attached to it.
Another object of the present invention is to provide a hoop structure with enough depth such that a parabolic or spherical shaped reflective surface and its shaping system can be substantially contained within the interior of the hoop.
Still another object of the present invention is to provide a hoop structure which folds compactly yet which deploys to a relatively large size.